1. Field of Invention
The present invention relates to power conversion, and more particularly, to a primary side regulated power supply system with constant current output.
2. Description of Related Art
Power supplies are essential for many modern electronic devices. In some applications for a power supply, such as a battery charger or a light emitting diode (LED) ballast, the power supply should provide a constant current, as long as the load resistance is lower than a specific value. If load resistance is above this value, the output voltage needs to be constant or at least limited in value. In a typical implementation according to previously developed designs for such applications, a power supply has a transformer (with primary and secondary windings) and an optocoupler device. The load (e.g., battery) is connected to the secondary winding, and the optocoupler is used to provide feedback from the secondary side for monitoring the current provided to the load. The optocoupler is a separate component, and thus its addition increases the cost of implementing the power supply. Furthermore, implementations according to previously developed designs may also use a dedicated integrated circuit (IC) device which is specially designed for the desired application (e.g., battery charger or LED ballast). Such a dedicated IC device also increases the cost of implementing the power supply.